Proton conductor, production method thereof, and electrochemical device using the same

ABSTRACT

A proton conductor mainly contains a carbonaceous material derivative, such as, a fullerene derivative, a carbon cluster derivative, or a tubular carbonaceous material derivative in which groups capable of transferring protons, for example, —OH groups or —OSO 3 H groups are introduced to carbon atoms of the carbonaceous material derivative. The proton conductor is produced typically by compacting a powder of the carbonaceous material derivative. The proton conductor is usable, even in a dry state, in a wide temperature range including ordinary temperature. In particular, the proton conductor mainly containing the carbon cluster derivative is advantageous in increasing the strength and extending the selection range of raw materials. An electrochemical device, such as, a fuel cell, that employs the proton conductor is not limited by atmospheric conditions and can be of a small and simple construction. The proton conductor may contain a polymer in addition to the carbonaceous material derivative, which conductor can be formed, typically by extrusion molding, into a thin film having a large strength, a high gas permeation preventive ability, and a good proton conductivity.

RELATED APPLICATION DATA

This application is a division of Ser. No. 09/619,166, filed Jul. 19,2000 now U.S. Pat. No. 6,495,290.

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 09/396,866 filed on Sep. 15, 1999 now abandoned.

The present application claims priority to Japanese Patent ApplicationNo. H11-204038 filed on Jul. 19, 1999, Japanese Patent Application No.P2000-058116 filed on Mar. 3, 2000, and Japanese Patent Application No.P2000-157509 filed on May 29, 2000. The above-referenced Japanese patentapplications are incorporated herein by reference to the extentpermitted by law.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a proton conductor, a production methodthereof, and an electrochemical device using the proton conductor.

2. Description of the Prior Art

In recent years, as a polymer solid-state electrolyte type fuel cell hasbeen used to power cars, there has been known a fuel cell using apolymer material having a proton (hydrogen ionic) conductivity such as aperfluorosulfonate resin (for example, Nafion® produced by Du Pont).

As a relatively new proton conductor, there has also been known apolymolybdate having large amount of hydrated water such asH₃Mo₁₂PO₄₀·29H₂O or an oxide having a large amount of hydrated watersuch as Sb₂O₆·5.4H₂O.

The above-described polymer material and hydrated compounds eachexhibit, if placed in a wet state, a high proton conductivity at atemperature near ordinary temperature.

For example, the reason why the perfluorosulfonate resin can exhibit avery high proton conductivity even at ordinary temperature is thatprotons ionized from sulfonate groups of the resin are bonded(hydrogen-bonded) with moisture already entrapped in a polymer matrix ina large amount, to produce protonated water, that is oxonium ions(H₃O⁺), and the protons in the form of the oxonium ions can smoothlymigrate in the polymer matrix.

More recently, there has been also developed a proton conductor having aconduction mechanism quite different than that of each of theabove-described proton conductors.

That is to say, it has been found that a composite metal oxide having aperovskite structure, such as, SrCeO₃ doped with Yb, exhibits a protonconductivity without use of moisture as a migration medium. Theconduction mechanism of this composite metal oxide has been consideredsuch that protons are conducted while being singly channeled betweenoxygen ions forming a skeleton of the perovskite structure.

The conductive protons, however, are not originally present in thecomposite metal oxide but are produced by the following mechanism:namely, when the perovskite structure contacts the steam contained in anenvironmental atmospheric gas, water molecules at a high temperaturereact with oxygen deficient portions which have been formed in theperovskite structure by doping Yb or the like, to generate protons.

The above-described various proton conductors, however, have thefollowing problems.

The matrix material such as the above-identified perfluorosulfonateresin must be continuously placed in a sufficiently wet state during usein order to keep a high proton conductivity.

Accordingly, a configuration of a system, such as, a fuel cell usingsuch a matrix material, requires a humidifier and various accessories,thereby giving rise to problems in enlarging the scale of the system andraising the cost of the system.

The system using the matrix material has a further problem that therange of the operational temperature must be limited for preventing thefreezing or boiling of the moisture contained in the matrix.

The composite metal oxide having the perovskite structure has a problemthat the operational temperature must be kept at a high temperature of500° C. or more for ensuring an effective proton conductivity.

In this way, the related art proton conductors have the problems thatthe atmosphere dependence on the performance of each conductor becomeshigh, and more specifically, moisture or stream must be supplied to theconductor to ensure the performance of the conductor, and further, theoperational temperature of the conductor is excessively high or therange of the operational temperature is limited.

SUMMARY OF THE INVENTION

A first object of the present invention is to provide a proton conductorwhich is usable in a wide temperature range including ordinarytemperature and has a low atmosphere dependence, that is, it requires nomoisture despite whether or not the moisture is a migration medium; toprovide a method of producing the proton conductor; and to provide anelectrochemical device that employs the proton conductor. To meet thisobjective, the proton conductor includes a proton conductor materialthat at least has number of functional groups so as to be capable oftransferring hydrogen protons between the functional groups of theproton conductor material. The proton conductor material includes a widevariety of carbonaceous materials, examples of which are described ingreater detail below with respect to the various illustrativeembodiments of the present invention, such as, the first, second, thirdand fourth proton conductors, production methods and electrochemicaldevices thereof.

A second object of the present invention is to provide a protonconductor which exhibits a film formation ability while keeping theabove-described performance, to be thereby usable as a thin film havinga high strength, a gas permeation preventive or impermeable performance,and a good proton conductivity, to provide a method of producing theproton conductor, and to provide an electrochemical device using theproton conductor.

The present invention provides a first proton conductor mainlycontaining a fullerene derivative obtained by introducing a number offunctional groups so as to be capable of transferring protons betweenthe functional groups of the fullerene derivative. The fullerenederivative includes a fullerene molecule or a plurality of fullerenemolecules that each contain the functional groups so as to provide thefullerene derivative with the desirable proton conductivity propertiesas discussed and will be discussed in greater detail below.

The present invention also provides a first method of producing a protonconductor, including the steps of: producing a fullerene derivative byintroducing functional groups so as to be capable of transferringprotons as previously discussed; and compacting a powder of thefullerene derivative into a desired shape.

The present invention also provides a first electrochemical deviceincluding: a first electrode, a second electrode, and a proton conductorheld between the electrodes, wherein the proton conductor mainlycontains a fullerene derivative as described above.

According to the first proton conductor of the present invention, sincethe conductor mainly contains the fullerene derivative having a protontransfer capability, protons are easily transferred or conducted, evenin a dry state, and further, the protons can exhibit a high conductivityin a wide temperature range (at least in a range of about 160° C. to−40° C.) that includes ordinary temperatures. While the first protonconductor of the present invention has a sufficient proton conductivityeven in a dry state, it can also have a proton conductivity in a wetstate. The moisture may come from the outside.

According to the first production method of the present invention, sincethe production method includes the steps of: producing a fullerenederivative by introducing functional groups as discussed and molding asubstance comprising the fullerene derivative, the proton conductor canbe efficiently produced having the above-described unique performancewithout use of any binder resin. The term “molding” means molding in ashape of film, pellet or the like. Therefore, compaction or filtrationor other like techniques are preferably available for producing theproton conductor.

According to the first electrochemical device of the present invention,since the proton conductor is held between the first and secondelectrodes, the first electrochemical device can eliminate the need fora humidifier and the like which are necessary for known fuel cells thatrequire moisture as a migration medium so as to enhance protonconductivity. Therefore, the device construction of the presentinvention has an advantageously smaller and more simplifiedconstruction.

The present invention also provides a second proton conductor thatincludes a polymer material in addition to the fullerene derivative aspreviously discussed.

The present invention also provides a second method of producing aproton conductor, including the steps of: producing a fullerenederivative by introducing functional groups as discussed above; andmixing the fullerene derivative with a polymer material and forming themixture into a desired shape, such as, a thin film.

The present invention also provides a second electrochemical deviceincluding: a first electrode, a second electrode, and a proton conductorheld between the electrodes, wherein the proton conductor mainlycontains a fullerene derivative as previously discussed, and a polymermaterial.

According to the second proton conductor of the present invention, sincethe conductor contains the fullerene derivative and a polymer material,it can exhibit not only an effect (high proton conductivity) comparableto that of the first proton conductor, but also a film formation abilityunlike the first proton conductor that only contains the fullerenederivative. The second proton conductor, thus, can be effectively usedas a thin film having a high strength, a gas permeation preventiveability, and a high proton conductivity.

According to the second production method of the present invention,since the method includes the steps of: producing a fullerenederivative, and mixing the fullerene derivative with a polymer materialthereby molding the mixture into a desired shape, such as, a thin film,it can efficiently produce the proton conductor having the above uniqueperformance in the form of a thin film. The term “molding” means moldingin a desired shape by squeezing-out, compacting, coating or the like asfurther detailed above.

According to the second electrochemical device of the present invention,since the proton conductor that contains the fullerene derivative isheld between the first and second electrodes, the second electrochemicaldevice can exhibit an effect comparable to that of the firstelectrochemical device, since the proton conductor also contains thepolymer material, the second electrochemical device can exhibit the samedesirable effects as the second proton conductor.

The present invention also provides a third proton conductor thatincludes a carbon cluster derivative which has a number of functionalgroups so as to be capable of transferring protons between thefunctional groups of the carbon cluster derivative. The carbon clusterderivative includes a cluster or a plurality of clusters as its basematerial. The clusters each mainly or substantially contain a number ofcarbon atoms, preferably, on order of several to several hundred carbonatoms.

The present invention also provides a third method of producing a protonconductor, including the steps of: producing clusters of carbon atoms byan arc discharge method using a carbon-based electrode; and subjectingthe carbon powder of the clusters to acid treatment or the like, tointroduce functional groups to the carbon powder so as to form thecarbon cluster derivative that is capable of transferring protons aspreviously discussed.

The present invention also provides a third electrochemical deviceincluding: a first electrode, a second electrode, and a proton conductorheld between the electrodes, wherein the proton conductor mainlycontains a carbon cluster derivative obtained by introducing functionalgroups to a cluster or a number of clusters that are the base materialof the carbon cluster derivative as discussed.

The present invention has uniquely discovered that it is required toform proton conductive paths (migration sites or channels) in thecarbonaceous material of the proton conductor as much as possible forimparting a good proton conductivity to the proton conductor. To meetsuch a requirement, it is necessary to introduce two or more functionalgroups that are capable of transferring protons, for example, on asurface of each of the clusters or a number of clusters, such as, anumber of carbon clusters of the carbon cluster derivative. The carboncluster is preferably made as small as possible. In this way, the carbonclusters can exhibit a desirable proton conductivity when combined inbulk to form the carbon cluster derivative of the proton conductor.

The cluster of the present invention generally means an aggregate inwhich atoms on order of several hundred are bonded or aggregated to eachother. The aggregate improves the proton conductivity and also ensures asufficient film strength while maintaining its chemical property to bethereby easily formed into a layer. The “cluster mainly or substantiallycontaining carbon atoms” means an aggregate in which a number of carbonatoms, preferably on order of several hundred, are closely bonded toeach other irrespective of the typically known molecular bonding thatoccurs between carbon atoms. Although this type of cluster contains alarge number of carbon atoms, it is not limited only to carbon atoms andmay include a variety of other atoms within its aggregate structure.Hereinafter, a cluster aggregate that contains a large number of carbonatoms—yet may also contain other atoms—is referred to as a “carboncluster”.

According to the third proton conductor of the present invention, theconductor mainly contains a carbon cluster derivative that has achemical structure which allows protons to be easily transferred asdiscussed, even in a dry state, with a result that the third protonconductor can exhibit effects, such as, a desirable proton conductivity,which are similar to those of the first proton conductor. In addition,the carbon cluster derivative may include clusters or carbon clustersthat contain a variety of different carbonaceous materials—examples ofwhich are discussed below.

According to the third production method of the present invention, sincethe production method produces the clusters or carbon clusters by makinguse of the arc discharge method using a carbon based electrode andsubjects the carbon clusters or clusters to at least acid treatment, itcan efficiently produce the carbon cluster derivative of the protonconductor having the above-described unique properties at a low cost.

According to the third electrochemical device of the present invention,since the above proton conductor is held between the first and secondelectrodes, the third electrochemical device can exhibit effects similarto those of the first electrochemical device.

The present invention also provides a fourth proton conductor mainlycontaining a tubular carbonaceous material derivative that includesfunctional groups so as to be capable of transferring protons betweenthe functional groups of the tubular carbonaceous material derivative ina similar fashion as protons are transferred on the proton conductor ofthe previously discussed embodiments, namely the first, second, andthird proton conductors, production methods, and electrochemical devicesthereof.

The present invention also provides a fourth method of producing aproton conductor that includes the steps of preparing a halogenated ornon-halogenated tubular carbonaceous material as a raw material; andintroducing functional groups onto the tubular carbonaceous material bysubjecting the material to hydrolysis and/or acid treatment or plasmatreatment so as to form the tubular carbonaceous material derivative.

The present invention also provides a fourth electrochemical device thatincludes a first electrode, a second electrode and a proton conductorthat is positioned between the electrodes wherein the proton conductormainly contains the tubular carbonaceous material derivative aspreviously discussed.

The tubular carbonaceous material derivative of the fourth embodimentsexhibits similar desirable and advantageous properties as the protonconductor materials of the previously discussed embodiments, such as,these materials provide a medium through which protons migrate easilyeven under a dry state.

As previously discussed, the principal reason why the proton conductorsof the present invention can exhibit such an excellent proton migrationcharacteristic is that a large number of functional groups, such as,hydroxyl and —OSO₃H groups, can be introduced to the tubularcarbonaceous material of the tubular carbonaceous material derivatives.

The tubular carbonaceous material derivative of the fourth embodimentincludes a carbon nano-tube (CNT) material, such as, a single wallcarbon nano-tube material (SWCNT), a multi-wall carbon nano-tubematerial (MWCNT), a carbon nano-fiber material (CNF), or other liketubular carbonaceous material.

The tubular carbonaceous material is characterized in that a ratio of anaxial length to a diameter of the tubular carbonaceous material is verylarge, and further the tubular carbonaceous molecules of this materialare entangled in a complicated form or structure that is inherent tothis kind of material. Accordingly, a large number of the functionalgroups can be introduced onto the surfaces of the tubular carbonaceousmolecules of these carbonaceous materials (see FIGS. 20-22).

In particular, the tubular carbonaceous material of the fourthembodiment makes it possible to increase the number of stable protonsites from which the protons can singly migrate without the use ofcarrier molecules, such as, water, and to continuously distribute thestable proton sites over an entire region of the material.

The fourth method of producing a proton conductor that includes atubular carbonaceous material derivative as discussed can be easilyproduced by preparing a halogenated or non-halogenated tubularcarbonaceous material; then subjecting the material to an acid treatmentor hydrolysis and an acid treatment or a plasma treatment. This materialcan then be easily formed into a film by dispersing the tubularcarbonaceous material derivative within a liquid such as water and thenfiltering the dispersion of the derivative.

The film thus formed, in which tubular molecules are entangled, has alarge strength, a high stability, and a good proton conductivity. Whenused for a general electrochemical device, the proton conductor isrequired to be configured as an aggregate of the tubular carbonaceousmaterial derivative, and in particular, when used for a fuel cell, theproton conductor is required to be configured as a thin film having ahigh stability, a high density, a large strength, and a good protonconductivity. Accordingly, it is apparent that the film of the tubularcarbonaceous material derivative according to the present invention isparticularly suitable for such an application.

The film can then be used for an electrochemical device wherein theproton conductor of the electrochemical device is formed of the film. Inthis way, the film is mounted as the proton conductor between the firstand second electrodes of the electrochemical device such that it ispossible to maintain desirable proton conductivity for a long period oftime without the need of using any external migration medium, such as,moisture so as to enhance proton conductivity.

DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are views showing a structure of a polyhydroxylatedfullerene molecule as examples of molecules of a fullerene derivative ofthe present invention;

FIGS. 2A, 2B, and 2C illustrate further examples of molecules of thefullerene derivative of the present invention, wherein FIGS. 2A-2C showa fullerene derivative that includes fullerene molecules which contain—OH groups, —OSO₃H groups, and Z groups, respectively;

FIGS. 3A and 3B illustrate examples of fullerene molecules;

FIG. 4 shows examples of carbon clusters of a carbon cluster derivativeof the third proton conductor of the present invention;

FIG. 5 shows further examples of carbon clusters that have partialfullerene structures;

FIG. 6 shows still further examples of carbon clusters that have diamondstructures;

FIG. 7 shows additional examples of carbon clusters which are bonded toeach other;

FIG. 8 is a schematic view of an example of a proton conductor of thepresent invention;

FIG. 9 is a sectional view showing a fuel cell that employs a protonconductor of the present invention;

FIGS. 10A and 10B are diagrams depict equivalent circuits of aexperimental pellets in Inventive Example 1 and Comparative Example 1;

FIG. 11 is a graph showing a result of measuring the complex impedancesof a pellet (a proton conductor containing a fullerene derivative) inInventive Example 1 and a pellet in Comparative Example 1;

FIG. 12 is a graph showing a temperature dependence on the protonconductivity of the pellet in Inventive Example 1;

FIG. 13 is a diagram showing results of the generating electricityexperiment using the fullerene derivative in Inventive Example 1.

FIG. 14 is a graph showing a result of measuring the complex impedanceof a pellet (a proton conductor containing a fullerene derivative and apolymer material) in Inventive Example 4 and a pellet in ComparativeExample 2;

FIG. 15 is a graph showing a temperature dependence on the protonconductivity of the pellet in Inventive Example 4;

FIG. 16 is a graph showing a TOF-MS spectrum of a carbon powder producedby an arc discharge process using a carbon electrode;

FIG. 17 is a sectional view of a hydrogen-air cell that employs a protonconductor of the present invention;

FIG. 18 is a schematic configuration view of another electrochemicaldevice using the proton conductor of the present invention;

FIG. 19 is a schematic configuration view of a further electrochemicaldevice using a proton conductor of the present invention.

FIG. 20 illustrates a tubular carbonaceous material derivative of thepresent invention;

FIG. 21 further illustrates a number of tubular carbonaceous moleculesof the tubular carbonaceous material derivative as shown in FIG. 20;

FIG. 22 illustrates another example of tubular carbonaceous molecules ofa tubular carbonaceous material derivative;

FIG. 23 is a graph that depicts the measuring a complex impedance of afilm used in Inventive Example 10;

FIGS. 24A and 24B each illustrate examples of tubular carbonaceousmaterials of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings.

A first proton conductor according to a first embodiment of the presentinvention mainly contains a fullerene derivative that includes a numberof functional groups so as to be capable of transferring protons betweenthe functional groups of the fullerene derivative.

According to this embodiment, the kind of fullerene molecule ormolecules used as a base material for the fullerene derivative to whichfunctional groups capable of transferring protons are introduced is notparticularly limited insofar as the fullerene molecules arecharacterized as a spherical carbon cluster or carbon clusters thatgenerally include the C₃₆, C₆₀ (see FIG. 3A), C₇₀ (see FIG. 3B), C₇₆,C₇₈, C₈₀, C₈₂, and C₈₄ fullerene molecules. It should be noted that amixture of these fullerene molecules or other like fullerene moleculesmay also be used as the base material of the fullerene derivative.

The fullerene molecule was found in the mass spectrum of a beam ofcarbon cluster created by laser abrasion of graphite in 1985. (H. W.Kroto, J. R. Heath, S. C. O'Brien, R. F. Curl and R. E. Smalley, Nature,318, 162 (1985)). The method of producing the fullerene molecules by arcdischarge of a carbon electrode was established five years later in1990. Ever since the establishment of the practical production method,the fullerene molecules have become a focus of attention as acarbon-based semiconductor material or the like.

The present invention has uniquely and advantageously examined theproton conductivities of derivatives of these fullerene molecules, andfound that a polyhydroxylated fullerene obtained by introducing hydroxylgroups to a number of carbon atoms of a fullerene molecule or moleculesexhibits, even in a dry state, a high proton conductivity in a widetemperature range including an ordinary temperature region, that is, atemperature range from less than the freezing point of water to morethan the boiling point of water (at least −40° C. to 160° C.), andfurther found that the proton conductivity becomes higher whenhydrogensulfate ester groups, namely, —OSO₃H groups, are introduced, inplace of the hydroxyl groups, to the fullerene molecule or molecules.

To be more specific, the polyhydroxylated fullerene or fullernol is ageneric name of a fullerene-based compound that has a structure in whicha plurality of hydroxyl groups are added to the fullerene molecule ormolecules as shown in FIGS. 1A and 1B. Of course, with respect to thenumber, arrangement, and the like of the hydroxyl groups of thefullerene molecule, some variations can be considered. The firstsynthesis example of the polyhydroxylated fullerene has been reported byChiang, et al. in 1992. (L. Y. Chiang, J. W. Swirczewski, C. S. Hsu, S.K. Chowdhury, S. Cameron and K. Creengan, J. Chem. Soc, Chem. Commun.,1791 (1992)). Since this report, the polyhydroxylated fullerene thatcontains a specific amount or more of the hydroxyl groups has become afocus of attention, particularly, in terms of its water-soluble ability,and has been studied mainly in the biotechnological field.

In an embodiment, the present invention has newly discovered that afullerene derivative can be formed from an aggregate of thepolyhydroxylated fullerene molecules, as schematically shown in FIG. 2A,in which the hydroxyl groups of each of these molecules adjacent to eachother (in the figure, ◯ designates the polyhydroxylated fullerenemolecule) act on each other, thereby exhibiting a high protonconductivity (that is, a high transferability of H⁺ between the phenolichydroxyl groups of the polyhydroxylated fullerene molecule or molecules)within the bulk or aggregate of the polyhydroxylated fullerenemolecules.

As the first proton conductor in this embodiment, the aggregate offullerene molecules wherein each or a number of the molecules have aplurality of —OSO₃H groups may be used in place of the aggregate ofpolyhydroxylated fullerene molecules as previously discussed. Thefullerene-based compound in which the OH groups are replaced with the—OSO₃H groups as show in FIG. 2B, that is, ahydrogensulfate-esterificated fullerenol (polyhydroxyl hydrogen sulfatedfullerene) was reported by Chiang, et al. in 1994. (L. Y. Chiang, L. Y.Wang, J. W. Swirczewski, S. Soled and S. Cameron, J. Org. Chem. 59, 3960(1994)). The molecules of polyhydroxyl hydrogen sulfated fullerene maycontain only the —OSO₃H groups or contain a number of the —OSO₃H groupsand a number of the hydroxyl groups.

In the case of preparing the fullerene derivative of the presentinvention, an aggregate of a large number of fullerene derivativemolecules that contain the hydroxyl groups or —OSO₃H groups orcombinations thereof is prepared. Since the protons derived from a largeamount of hydroxyl groups or —OSO₃H groups or combinations thereof thatare originally contained in the molecules directly migrate, the protonconductivity of the bulk or aggregate of these fullerene molecules isself-determined without the need of entrapment of hydrogen resultingfrom steam molecules or protons from an atmosphere and also without theneed of supply of water from an external environment, particularly, theneed of absorption of water or the like from atmospheric air. In otherwords, the proton conductivity of the aggregate of the fullerenemolecules that contain the functional groups is not limited by theenvironmental atmosphere. Further, the fullerene molecules as the basematerial of the fullerene derivative particularly have an electrophilicproperty, which property may allow not only the —OSO₃H groups having ahigh acidity but also the hydroxyl groups to largely promote theionization of hydrogen. This is one of the reasons why the first protonconductor of an embodiment of the present invention exhibits anexcellent proton conductivity.

According to the first proton conductor of an embodiment of the presentinvention, since a large amount of hydroxyl groups or —OSO₃H groups orcombinations thereof can be introduced to each or a number of thefullerene molecules of the fullerene derivative, the numerical densityof protons related to conductivity per unit volume of the conductorbecomes very large. This is another reason why the first protonconductor in this embodiment exhibits an effective conductivity.

Since the fullerene molecule or molecules of the fullerene derivative ofthe first proton conductor in this embodiment are mostly orsubstantially composed of carbon atoms, the fullerene derivative islight in weight, not easily decomposed, and relatively pure, that is,relatively free of contaminants that may negatively impact its desirableproton conductivity properties. In addition, the cost that is requiredto produce the fullerene derivative has been rapidly lowered.Accordingly, the fullerene may be regarded as a desirable carbonaceousmaterial based on resource, environmental, economic or other desirableconsiderations as previously discussed.

As a result of the present invention, it is further discovered that thefunctional groups, as discussed above, are not limited to the hydroxylor —OSO₃H functional groups.

To be more specific, the functional groups can be expressed by achemical formula of —XH where X is an arbitrary atom or atomic grouphaving a bivalent bond, and further the group can be expressed by achemical formula of —OH or —YOH where Y is an arbitrary atom or atomicgroup having a bivalent bond. In particular, the functional groups arepreferably at least one of the —OH and —OSO₃H, and —COOH, —SO₃H and—OPO(OH)₃ functional groups.

According to this embodiment, electron attractive groups, such as, nitrogroups, carbonyl groups and carboxyl groups, nitrile groups, alkylhalide groups or halogen atoms (fluorine or chlorine atoms) may bepreferably introduced together with the functional groups, to carbonatoms of the fullerene molecule or molecules. FIG. 2C shows a fullerenemolecule to which Z is introduced in addition to —OH, where Z representsat least one of the —NO₂, —CN, —F, —Cl, —COOR, —CHO, —COR, —CF₃, or—SO₃CF₃ (R is an alkyl group) electron attractive groups. With thepresence of the electron attractive groups in addition to the functionalgroups, it is easy for protons to be released from the functional groupsand to be transferred between the functional groups by the electronattractive effect of the electron attractive groups.

According to this embodiment, the number of the functional groups can befreely selected insofar as it is less than the number of the carbonatoms of the fullerene molecule or molecules, and preferably may include5 functional groups or more. To keep the π electron characteristic ofthe fullerene molecule for achieving the effective electron attractiveability, the number of functional groups is more preferably half or lessthan half of the number of carbon atoms of a fullerene molecule ormolecules.

To synthesize the above-described fullerene derivative used for thefirst proton conductor of an embodiment, as will be described later withreference to examples, desired functional groups may be introduced tocarbon atoms of each or a number of the fullerene molecules of thefullerene derivative by subjecting a powder of the fullerene moleculesto known treatments, such as, acid treatment and hydrolysis suitably incombination.

After treatment, the powder of the fullerene derivative thus obtainedcan be compacted into a desired shape, for example, into a pellet. Thecompacting of the powder can be performed without use of any binder,which is effective to enhance the proton conductivity and to reduce theweight of the proton conductor, resulting in a molded material thatsubstantially contains the fullerene derivative.

The first proton conductor in this embodiment can be suitably used forvarious electrochemical devices. For example, the present invention canbe preferably applied to an electrochemical device having a basicstructure that includes first and second electrodes and a protonconductor held therebetween, wherein the proton conductor is configuredas the first proton conductor in this embodiment.

To be more specific, the first proton conductor in this embodiment canbe preferably applied to an electrochemical device in which at least oneof the first and second electrodes is a gas electrode, or anelectrochemical device in which at least one of the first and secondelectrodes is an active electrode.

Hereinafter, an example in which the first proton conductor in thisembodiment is applied to a fuel cell will be described.

FIG. 8 is a schematic view showing the proton conductance of the fuelcell in which a proton conducting portion 1 is held between a firstelectrode (for example, hydrogen electrode) 1 and a second electrode(for example, oxygen electrode) 3, wherein protons dissociated ortransferred in the proton conducting portion 1 migrate from the firstelectrode 2 side to the second electrode 3 side along the directionshown by an arrow in FIG. 8.

FIG. 9 is a schematic view showing one example of the fuel cell usingthe first proton conductor in this embodiment. The fuel cell isconfigured such that a negative electrode (fuel electrode or hydrogenelectrode) 2 to or in which a catalyst 2 a is closely overlapped ordispersed and which has a terminal 8 faces to a positive electrode(oxygen electrode) 3 to or in which a catalyst 3 a is closely overlappedor dispersed and which has a terminal 9, and a proton conducting portion1 is held therebetween. Upon use of the fuel cell, hydrogen is suppliedfrom an inlet 12 on the negative electrode 2 side, and is dischargedfrom an outlet 13 (which is sometimes not provided) on the negativeelectrode 2 side. During a period in which fuel (H₂) 14 passes through aflow passage 15, protons are generated. The protons migrate togetherwith protons generated in the proton conducting portion 1, onto thepositive electrode 3 side, and react with oxygen (air) 19, which hasbeen supplied in a flow passage 17 from an inlet 16 and flows toward anoutlet 18, to generate a desired electromotive force.

According to the fuel cell having the above configuration, since theprotons generated in the proton conducting portion 1 migrate, togetherwith the protons supplied from the negative electrode 2 side, onto thepositive electrode 3 side, the proton conductivity becomes higher. As aresult, it is possible to eliminate the need of any humidifier or otherwater source or other external migration medium and hence to simplifythe configuration of the system and reduce the weight of the system.

A second embodiment of the present invention will be described below.The second embodiment is different from the first embodiment in that theabove-described fullerene derivative is used in combination with apolymer material. However, the proton conductor of the second embodimentessentially has the same proton conductivity features of the firstembodiment.

A second proton conductor in this embodiment contains theabove-described derivative and a polymer material.

The polymer material may be one kind or two kinds or more known polymershaving a film formation ability. The content of the polymer material isgenerally 20 wt % or less. If the content is more than 20 wt %, theproton conductivity of the fullerene derivative may degrade.

Since the second proton conductor in this embodiment contains thefullerene derivative, it can exhibit a proton conductivity comparable tothat of the first proton conductor of the first embodiment.

While the first proton conductor in the first embodiment containing onlythe fullerene derivative is used as a compacted powder as describedabove, the second proton conductor in this embodiment having a filmformation ability derived from the polymer material can be used as aflexible proton conductive thin film having a large strength and a gasimpermeable property. In general, the thickness of the proton conductivethin film is 300 μm or less.

The kind of polymer material is not particularly limited insofar as itdoes not obstruct the proton conductivity as much as possible (due tothe reaction with the fullerene derivative or the like) and has a filmformation ability, but may be generally selected from polymers having noelectronic conductivity and exhibiting a good stability. Examples ofthese polymers may include polytetrafluoroethylene, polyvinylidenefluoride, and polyvinyl alcohol. The reason why polytetrafluoroethylene,polyvinylidene fluoride or polyvinyl alcohol are suitable for the secondproton conductor in this embodiment will be described below.

The reason why polytetrafluoroethylene is suitable for the second protonconductor is that it has a good film formation ability. Even by addingpolytetrafluoroethylene to the fullerene derivative in an amount smallerthan that of another polymer material, it is possible to easily form athin film of the second proton conductor having a large strength. Thecontent of polytetrafluoroethylene includes 3 wt % or less, preferably,in a range of 0.5 to 1.5 wt %. By adding polytetrafluoroethylene to thefullerene derivative in an amount within the above range, the thin filmof the second proton conductor has a thickness that ranges from 1 μm to100 μm.

The reason why polyvinylidene fluoride or polyvinyl alcohol are suitablefor the second proton conductor is that it is effective to form a protonconductive thin film having a good gas permeation preventive ability.The content of polyvinylidene fluoride or polyvinyl alcohol may rangefrom 5 to 15 wt %. If the content of polyvinylidene fluoride orpolyvinyl alcohol is less than the lower limit of the above range, theremay occur an adverse effect exerted on the film formation.

The thin film of the second proton conductor in this embodiment may beobtained by using a known film formation technique, such as, extrusionmolding.

The second proton conductor in this embodiment can be preferably appliedto the electrochemical device to which the first proton conductor in thefirst embodiment is applied.

That is to say, in the electrochemical device to which the firstembodiment is applied, in which the first proton conductor is heldbetween the first and second electrodes, the first proton conductor maybe replaced with the second proton conductor in this embodiment.

FIG. 17 is a schematic view showing a hydrogen-air cell to which thesecond proton conductor in this embodiment is applied. In this device, ahydrogen electrode 21 faces to an air electrode 22 with a protonconductor 20 formed into a thin film (configured as the second protonconductor) held therebetween, and the outsides of these electrodes 21and 22 are held between a Teflon plate 24 a and a Teflon plate 24 bhaving a number of holes 25 and fixed thereto by way of bolts 26 a and26 b and nuts 27 a and 27 b, wherein a hydrogen electrode lead 28 a andan air electrode lead 28 b extending from the electrodes 21 and 22 areextracted to the outside of the cell.

FIG. 18 is a schematic view showing an electrochemical device to whichthe second proton conductor in this embodiment is applied. Referring toFIG. 18, a proton conductor 34 (configured as the second protonconductor) is held between a negative electrode 31 having on its innersurface a negative electrode active material layer 30 and a positiveelectrode (gas electrode) 33 having on its outer surface a gaspermeation support 32. The negative electrode active material may beconfigured as a hydrogen absorption alloy or a hydrogen absorption alloysupported by a carbon material such as a fullerene. The gas permeationsupport 32 may be configured as a porous carbon paper. The positiveelectrode 33 may be preferably formed by coating a paste of platinumsupported by a powder of carbon. Gaps between the outer ends of thenegative electrode 31 and the outer ends of the positive electrode 33are blocked by gaskets 35. In this electrochemical device, charging canbe performed by making water be present on the positive electrode 33side.

FIG. 19 is a schematic view showing an electrochemical device to whichthe second proton conductor in this embodiment is applied. Referring toFIG. 19, a proton conductor 41 formed into a thin film (configured asthe second proton conductor) is held between a negative electrode 38having on its inner surface a negative electrode active material layer37 and a positive electrode 40 having on its inner surface a positiveelectrode active material layer 39. The positive electrode activematerial is typically configured as a material mainly containing nickelhydroxide. Even in this electrochemical device, gaps between the outerends of the negative electrode 38 and the outer ends of the positiveelectrode 40 are blocked with gaskets 42.

Each of the above-described electrochemical devices using the secondproton conductor in this embodiment can exhibit a good proton conductiveeffect on the basis of the same mechanism as that of theelectromechanical device using the first proton conductor in the firstembodiment. Further, since the second proton conductor containing thefullerene derivative in combination with the polymer material having afilm formation ability, it can be formed into a thin film having a largestrength and a small gas permeability, and therefore, it can exhibit agood proton conductivity.

A third embodiment of the present invention will be described below. Thethird embodiment is different from the first and second embodiments inthat the proton conductor mainly contains a carbon cluster derivative orderivatives, but is the same or similar to the first and secondembodiments in other ways, such as, the basic function of the protonconduction mechanism.

A third proton conductor in this embodiment mainly contains a carboncluster derivative in which the functional groups are introduced to anumber of carbon atoms of each of the clusters or carbon clusters whichare used as a base material for the carbon cluster derivative.

The reason why the cluster(s) or carbon cluster(s) are used as the basematerial in this embodiment is that a large number of functional groupscan be introduced to each cluster or carbon cluster via their respectivecarbon atoms. By introducing a large number of functional groups ontothe cluster or carbon cluster, a desirable proton conductivity isachieved due to the fact that the introduction of a large number offunctional groups significantly increases the acidity of the solid-stateproton conductor. In addition, the increased acidity has little, if any,effect on the integrity of the chemical structure of the cluster orcarbon cluster because atoms of the carbon cluster or cluster are soclosely bonded to one another. With this closely-bonded chemicalstructure, the carbon cluster or cluster are superior in durability toother known carbonaceous or carbon-based materials, thereby resulting ina desirable film structure for the proton conductor.

The third proton conductor in this embodiment having the aboveconfiguration can exhibit, even in a dry state, a high protonconductivity similar to that of each of the first and second protonconductors in the first and second embodiments.

As defined above, the “carbon cluster” means an aggregate of up toseveral hundred carbon atoms that are closely bonded togetherirrespective of the carbon to carbon molecular-type bonding that existsbetween the carbon atoms. It should be noted that the carbon cluster,that is, an aggregate of that substantially contains carbon atoms is notnecessarily entirely composed of carbon atoms. Various types of carbonclusters or aggregates of carbon atoms are shown in FIGS. 4 to 7. Inthese figures, the functional groups, for example, hydroxyl groups, arenot shown.

FIG. 4 shows carbon clusters having spherical structures, spheroidstructures, and planar structures similar thereto. FIG. 5 shows carbonclusters that have a partially open spherical structure which ischaracterized by an open end or ends. During production of the fullerenemolecules by arc discharge, a large number of carbon clusters having aspherical structure with open ends are generated as sub-products. FIG. 6shows carbon clusters each having a diamond structure, in which most ofthe carbon atoms of the carbon cluster are in the SP³ bonding.

A carbon cluster material in which most of the carbon atoms are in theSP² bonding has a planar structure of graphite or has all or part of afullerene or nano-tube structure. While it is not a problem that thecarbon cluster material having a planar structure or graphite is used asthe base or other component of the proton conductor, the protonconductivity should be larger than an electronic conductivity in totalin the proton conductor.

On the contrary, a fullerene or nano-tube structure that has the SP²bonding often has no electronic conductivity because it also partiallycontains an element that exhibits the desirable SP³ bonding. While somenano-tube structure has an electronic conductivity, the electronicconductivity can be vanished or lessened by introducing theabove-mentioned functional groups to the nano-tube structure. Therefore,these carbon materials are desirable as the base of a proton conductor.

FIG. 7 shows carbon clusters which are bonded to each other. FIG. 7,thus, represents examples of carbon clusters that can be utilized tomake the carbon cluster derivative of the proton conductor in anembodiment of the third proton conductor of the present invention.

To form the third proton conductor in this embodiment, it is required tointroduce functional groups to the clusters or carbon clusters. Further,it may be desirable to further introduce electronic attractive groups toeach of the clusters or carbon cluster. The functional groups may beintroduced to each carbon cluster in accordance with the followingproduction method.

According to the production method of the present invention, a carboncluster derivative can be easily obtained by producing carbon clusterscomposed of carbon powder by arc discharge of a carbon-based electrode,and suitably subjecting the carbon clusters to acid treatment, typicallyusing sulfuric acid and hydrolysis, and also subjected to sulfonation orphosphatation so as to introduce the sulfur and phosphorus-basedfunctional groups, respectively.

The carbon cluster derivative can be compacted into a suitable shape,for example, into a pellet. According to the third proton conductor inthis embodiment, the length of the major axis of each of the carbonclusters as the base of the carbon cluster derivatives of the protonconductors may be 100 nm or less, preferably, 100 Å or less, and thenumber of functional groups to be introduced therein may be preferably 2or more.

The carbon cluster used for the third proton conductor may be of a cagestructure at least part of which has open ends. The carbon clustershaving such a case structure has a reactivity similar to that of afullerene and also has a higher reactivity at its defect portions, thatis, its open end portion or portions. Accordingly, the use of carbonclusters each having such a defect structure, that is, open end or ends,as the base of the third proton conductor can promote the introductionof functional groups by acid treatment or the like, that is, increasethe introduction efficiency of the functional groups, thereby enhancingproton conductivity of the third proton conductor. Further, it ispossible to synthesize a larger amount of carbon clusters as comparedwith fullerene molecules, and hence to produce the carbon clusters at avery low cost.

The kinds of functional groups and the electron attractive groups to beintroduced to each of the carbon clusters as the base of the thirdproton conductor in this embodiment may be the same as those describedabove.

The third proton conductor in this embodiment can be suitably applied tovarious kinds of electrochemical devices, such as, a fuel cell. In thiscase, the configuration of the electrochemical device may be basicallythe same as that of the electromechanical device to which the first orsecond proton conductor in the first or second embodiment is appliedexcept that the first or second proton conductor is replaced with thethird proton conductor. Since the third proton conductor in thisembodiment can also exhibit a good proton conductivity even in a drystate, it is possible to eliminate the need of providing any humidifieror other like instrument that produces an external migration, such as,water or steam, and hence to simplify the system configuration andreduce the weight of the system.

A fourth embodiment of the present invention will be described below inwhich the proton conductor includes a tubular carbonaceous materialderivative. The tubular carbonaceous material derivative includes atubular carbonaceous material as its base material. The tubularcarbonaceous material includes a CNT material that is composed ofnano-tube molecules that each have a diameter of about severalnanometers or less, typically, in a range of 1 to 2 nanometers. Inaddition to the CNT material, the tubular carbonaceous material includesa CNF material that is composed of nano-fiber molecules which each havea diameter of several nanometers or more which may reach up to 1 mm.Further, it is known that the CNT material includes a single-wall carbonnano-tube (SWCNT) material that is composed of nano-tube molecules eachbeing formed by a single layer or a multi-wall carbon nano-tube (MWCNT)that is composed of nano-tube molecules that are each formed of two ormore layers which are concentrically overlapped.

The configurations of the SWCNT and the MWCNT molecules are respectivelyshown in FIGS. 24A and 24B. In addition, the description of the CNT, theSWCNT and MWCNT materials are illustrative only wherein it is understoodthat the present invention is not limited to the same.

According to the fourth embodiment of the present invention, thefunctional groups that are introduced to the tubular carbonaceousmaterials in order to form the tubular carbonaceous material derivativesinclude the same functional groups as previously discussed in regards tothe other embodiment of the present invention. As illustrated, FIG. 20shows an example of a tubular carbonaceous material derivative thatcontains the hydroxyl functional groups. In addition, FIG. 21illustrates a number of the tubular carbonaceous molecules or tubularmolecules of the tubular carbonaceous material derivative as shown inFIG. 20. As well, FIG. 22 illustrates the tubular molecules of anothertubular carbonaceous material derivative that includes the —OSO₃Hfunctional groups. Such a tubular carbonaceous material derivative isproduced by preparing a halogenated tubular carbonaceous material andsubjecting the halogenated material to acid treatment by using sulfuricor nitric acid in order to introduce the —OSO₃H functional groups to thetubular carbonaceous material so as to form its derivative. In addition,a hydrolysis technique may be used to introduce hydroxyl groups insteadof the —OSO₃H functional groups. If hydrolysis is used, an acidtreatment may follow in order to substitute the hydroxyl groups fordifferent functional groups, such as, the —OSO₃H functional groups.

If a non-halogenated tubular carbonaceous material is used as a base orraw material so as to form the tubular carbonaceous material derivative,this material may be subjected to acid treatment by using sulfuric ornitric acid as previously discussed. With regards to the halogenatedtubular carbonaceous material, fluorine is preferably used.

The tubular carbonaceous material derivative can be produced not only bythe above described wet method but also by the following dry method thatutilizes plasma. In this method, a non-halogenated tubular carbonaceousmaterial is subjected to plasma treatment in an oxygen gas and thensubjected to further plasma treatment under a hydrogen gas in order tointroduce the functional groups, typically, hydroxyl groups to thetubular molecules of the tubular carbonaceous material.

The invention has examined the proton conductivities of these tubularcarbonaceous material derivatives and found that these materialsprovided a high proton conductivity under a varying temperature rangethat includes the ordinary temperature region, that is, a temperatureranging from less than the freezing point of water to more than theboiling point of water (at least −40° C. to 160° C. The presentinvention has further discovered that the proton conductivity is higherfor tubular carbonaceous material derivatives that include the hydrogensulfate as their groups in place of the hydroxyl groups.

In particular, the polyhydroxylated SWCNT material is a generic name ofa derivative that has a structure in which a plurality of hydroxylgroups are added to a number of tubular molecules so as to form theSWCNT material as illustrated in FIG. 20. Of course, with respect to thenumber, arrangement and the like of the hydroxyl groups, some variationsare considered to be within the scope of the present invention.

The present invention has newly discovered that an aggregate ofpolyhydroxylated tubular molecules, namely, a polyhydroxylated SWCNTmaterial, as illustrated in FIGS. 20 & 21, in which the hydroxyl groupsof the tubular molecules adjacent to each other act on each other toexhibit a high proton conductivity, that is, a high transfer ormigration ability of H⁺ or protons from the phenolic hydroxy groups thatare contained in each of the tubular molecules of the polyhydroxylatedSWCNT material or bulk material.

The proton conductor of the fourth embodiment includes the same type andarrangement of functional groups as the proton conductor of the otherembodiments. For example, the proton conductor may include functionalgroups such as hydroxyl groups, OSO₃H groups, and combinations of thesegroups thereof.

The proton conductivity of the tubular carbonaceous material derivativethat includes an aggregate of the tubular molecules having a number offunctional groups, like the proton conductivity of the other protonconductor embodiments, is not limited by the environmental surroundings.In this way, an additional source of protons from migrating mediums,such as, water is not necessary in order to realize the desirableeffects of the present invention. Similar to the other embodiments, thereason why the tubular carbonaceous material derivative can exhibit sucha desirable proton conductivity effect is that a large amount of thefunctional groups can be introduced to a number of the tubular moleculesof the tubular carbonaceous material so that the proton density whichcorresponds to the conductivity per unit volume of the conductor is verylarge in size.

In addition, the tubular carbonaceous material derivative is mostlycomposed of carbon atoms of each of the tubular molecules and thereforeis light in weight and does not decompose as readily nor contain anycontaminants. Moreover, the tubular carbonaceous material that is usedfor a base material for producing the derivative thereof can be producedby catalytic thermal decomposition of hydrocarbons at a low cost. As aresult, the tubular carbonaceous material is regarded as a material thatis desirable for reasons of resource, environment and economy. (CarbonVol. 36, No. 11, pp. 1603-1612, 1998, 1978, Eiseier Science Ltd.,Printed in Great Britain).

As previously discussed, the tubular carbonaceous material derivativeincludes a number of functional groups that provide the desirable protonconductivity effect. The functional groups of this derivative aresimilar in number and type and arrangement as the functional groups ofthe other embodiments as previously discussed. In addition, the tubularcarbonaceous material derivatives can include an electron attractivegroup as previously discussed in the other embodiments of the protonconductor. With the presence of the electron attractive groups, theproton can more easily migrate or transfer between functional groups ofthe derivative due to the electron attractive effect of the electronattractive groups.

With respect to the number of functional groups of the tubularcarbonaceous material derivative, the number is limited to the extentthat it is less than the number of carbon atoms of the tubularcarbonaceous material derivative. In addition, the number of functionalgroups may be limited to the extent that is necessary to cancel theelectronic conductivity. For example, this number is preferably one ormore per ten carbon atoms for a CNT material.

In addition to the functional groups and electron attractive groups, theproton conductor that mainly contains the tubular carbonaceous materialderivatives may further contain another carbonaceous materialderivative, such as, a fullerene derivative that includes a number offunctional groups as previously discussed. Examples of fullerenemolecules that make-up the fullerene derivative have been previouslydiscussed and are further illustrated in FIGS. 3A and 3B.

By combining the tubular carbonaceous material with the fullerenematerial, the advantageous and desirable properties can be combined tomeet the needs for a variety of different applications of thesematerials. The tubular carbonaceous material forms a strong and stablefilm that is suitable for an electrochemical device due to the fact thatits axial length is much longer than its diameter and that the tubularmolecules are entangled in a complicated form. This structure isstronger than an aggregate of a fullerene derivative that includesspherical fullerene molecules. However, the fullerene derivative moreeasily reacts with the functional groups and thereby a higher protonconductivity can be obtained on these materials versus the tubularcarbonaceous materials.

According to the present invention, tubular carbonaceous materialderivatives may be desirably formed as a film to be used for anelectrochemical device such as a fuel cell. These materials can beformed as a film by a known extrusion molding technique and morepreferably by dispersing the tubular carbonaceous material derivative ina liquid and filtering the dispersion. A solvent such as water isgenerally used as the liquid. However, the liquid is not particularlylimited insofar as the derivative can be dispersed in the liquid.

By filtering the dispersion, the tubular carbonaceous materialderivative is deposited in a film shape on the filter. The film does notcontain any binder and is composed of only the tubular carbonaceousmaterial derivative wherein the tubular molecules are entangled incomplicated form. Such a film has a very high strength and can be easilypeeled from the filter. In this case, if the fullerene derivative isdispersed in combination with the tubular carbonaceous materialderivative in the liquid, it is possible to easily form a composite filmwhich is composed of a combination of these materials which again doesnot contain any binder.

As previously discussed, the proton conductor that mainly includes atubular carbonaceous material derivative is preferably used for a fuelcell. The fuel cell application of this material is similar to theapplication of the other previously discussed materials. The presentinvention will be more clearly understood with reference to thefollowing examples:

I. Fullerene Derivative

<Synthesis of Polyhydroxylated Fullerene>

The synthesis of polyhydroxylated fullerene was performed with referenceto L. Y. Chaing, L. Y. Wang, J. W. Swircczewski, S. Soled and S.Cameron, J. Org. Chem. 59, 3960 (1994). First, 2 g of a powder of amixture of C₆₀ and C₇₀ containing about 15% of C₇₀ was put in 30 ml offuming sulfuric acid, and was stirred for three days while being kept ina nitrogen atmosphere at 60° C. The reactant was put little by little indiethyl ether anhydride cooled in an ice bath, and the deposit wasfractionated by centrifugal separation, cleansed twice by diethyl etherand twice by a mixture of diethyl ether and acetonitrile at a mixingratio of 2:1, and dried under a reduced pressure at 40° C. The depositthus cleaned and dried was put into 60 ml of ion exchange water, andstirred for 10 hours at 85° C. while being subjected to bubbling usingnitrogen. The reactant was subjected to centrifugal separation, toseparate a deposit, and the deposit was cleaned several times by purewater, repeatedly subjected to centrifugal separation, and dried under areduced pressure at 40° C. A brown powder thus obtained was subjected toFT-IR measurement. As a result, the IR spectrum of the brown powdernearly conformed to that of C₆₀ (OH)₁₂ shown in the above document, andtherefore, it was confirmed that the powder was the polyhydroxylatedfullerene as the target material.

<Production of Pellet of Aggregate of Polyhydroxylated Fullerene>

Next, 90 mg of the powder of the polyhydroxylated fullerene was pressedin one direction at a pressure of about 5 tons/cm² into a circularpellet having a diameter of 15 mm. Since the compactivity of the powderof polyhydroxylated fullerene was excellent although the powdercontained no binder resin, the powder of the polyhydroxylated fullerenecould be easily formed into a pellet having a thickness of about 300 μm.Such a pellet is taken as a pellet in Inventive Example 1.

<Synthesis (Part 1) of Poly-Hydrogen-Sulfated Fullerene>

The synthesis of a poly-hydrogen-sulfated fullerene or hydrogen sulfatedfullerene was performed with reference to the above-described document.First. 1 g of a powder of a polyhydroxylated fullerene was put in 60 mlof fuming sulfuric acid, and was stirred for three days while being keptin a nitrogen atmosphere at ordinary temperature. The reactant was putlittle by little in diethyl ether anhydride, cooled in an ice bath, andthe deposit was fractionated by centrifugal separation, cleansedthree-times by diethyl ether and twice by a mixture of diethyl ether andacetonitrile at a mixing ration of 2:1, and dried under a reducedpressure at 40° C. A powder thus obtained was subjected to FT-IRmeasurement. As a result, the IR spectrum of the powder nearly conformedto that of a poly-hydrogen-sulfated fullerene in which the hydroxylgroups were entirely replaced with hydrogen sulfated groups, i.e. —OSO₃Hgroups, shown in the document, and therefore, it confirmed that thepowder was the poly-hydrogen-sulfated fullerene as the target material.The above-described reaction is represented, for example, concerning C₆₀(OH)_(y) as follows (here and hereinafter):

<Production (Part 1) of Pellet of Aggregate of Poly-hydrogen-sulfatedFullerene>

Next, 70 mg of the powder of poly-hydrogen-sulfated fullerene waspressed in one direction at a pressure of about 5 tons/cm² into acircular pellet having a diameter of 15 mm. Since the compactivity ofthe powder of poly-hydrogen-sulfated fullerene was excellent althoughthe powder contained no binder resin, the powder ofpoly-hydrogen-sulfated fullerene could be easily formed into a pellethaving a thickness of about 300 μm. Such a pellet is taken as a pelletin Inventive Example 2.

<Synthesis (Part 2) of Partially Hydrogensulfate-EsterificatedPolyfullerene Hydride (Polyhydroxyl Hydrogen Sulfated Fullerene)>

First, 2 g of powder of a mixture of C₆₀ and C₇₀ containing about 15% ofC₇₀ was put in 30 ml of fuming sulfuric acid, and was stirred for threedays while being kept in a nitrogen atmosphere at 60° C. The reactantwas put little by little in diethyl ether cooled in an ice bath. Itshould be noted that diethyl ether not subjected to dehydration is used.The deposit thus obtained was fractionated by centrifugal separation,cleaned three times by diethyl ether and twice by a mixture of diethylether and acetonitrile at a mixing ratio of 2:1, and dried under areduced pressure at 40° C. A powder thus obtained was subjected to FT-IRmeasurement. As a result, the IR spectrum of the powder nearly conformedto that of a fullerene derivative containing both of the hydroxyl andOSO₃H groups shown in the document, and therefore, it was confirmed thatthe powder was the polyhydroxyl hydrogen sulfated fullerene as thetarget material. The above-described reactions are represented, forexample, concerning C₆₀ as follows (here and hereinafter):

<Production (Part 2) Pellet of Aggregate of Polyhydroxyl HydrogenSulfate Fullerene>

Next, 80 mg of the powder of a polyhydroxyl hydrogen sulfated fullerenewas pressed in one direction at a pressure of about 5 tons/cm² into acircular pellet having a diameter of 15 mm. Since the compactivity ofthe powder of polyhydroxyl hydrogen sulfated fullerene was excellentalthough the powder contained no binder resin, the powder of thepolyhydroxyl hydrogen sulfated fullerene could be easily formed into apellet having a thickness of about 300 μm. Such a pellet is taken as apellet in Inventive Example 3.

For comparison, 90 mg of a powder of the fullerene molecules used as athe raw material for synthesis in the above examples was pressed in onedirection at a pressure of about 5 tons/cm² into a circular pellethaving a diameter of 15 mm. Since the compactivity of the powder of thefullerene molecules was relatively excellent although the powdercontained no binder resin, the powder of the fullerene molecules couldbe relatively easily formed into a pellet having thickness of about 300μm. Such a pellet is taken as a pellet in Comparative Example 1.

<Measurement of Proton Conductivities of Pellets of Inventive Examplesand Comparative Example>

To measure a proton conductivity of each of the pellets of InventiveExample 1-3 and Comparative Example 1, both sides of the pellet wereheld between aluminum plates each having the same diameter as that ofthe pellet, that is, 15 mm, and AC voltages (amplitude: 0.1 V) atfrequencies ranging from 7 MHz to 0.01 Hz are applied to the pellet, tomeasure a complex impedance at each frequency. The measurement wasperformed under a dry atmosphere.

With respect to the above impedance measurement, a proton conductingportion 1 of a proton conductor composed of the above pelletelectrically constitutes an equivalent circuit shown in FIG. 10A, inwhich capacitances 6 and 6′ are formed between first and secondelectrodes 2 and 3 with the proton conducting portion 1 expressed by aparallel circuit of a resistance 4 and a capacitance 5 heldtherebetween. In addition, the capacitance 5 designates a delay effect(phase delay at a high frequency) upon migration of protons, and theresistance 4 designates a parameter of difficulty of migration ofprotons.

The measured impedance Z is expressed by an equation Z=Re(Z)+i·Im(Z).The frequency dependency on the proton conducting portion expressed bythe above equivalent circuit was examined.

In addition, FIG. 10B shows an equivalent circuit of a proton conductor(Comparative Example to be described later) using the typical fullerenemolecules without functional groups.

FIG. 11 shows results of measuring the impedances of the pellets ofInventive Example 1 and Comparative Example 1.

Referring to FIG. 11, for Comparative Example 1, the frequencycharacteristics of the complex impedance is nearly the same as thebehavior of a single capacitor, and the conductance of charged particles(electrons, ions and the like) of the aggregate of the fullerenemolecules is not observed at all; while, for Inventive example 1, theimpedance in a high frequency region depicts a flattened but very smoothsingle semi-circular arc, which shows the conductance of some chargedparticles in the pellet, and the imaginary number portion of theimpedance is rapidly raised in a low frequency region, which shows theoccurrence of blocking of charged particles between the aluminumelectrode and the pellet as gradually nearing the DC voltage. Withrespect to the blocking of the charged particles between the aluminumelectrode and the pellet in Inventive Example 1, the charged particleson the aluminum electrode side are electrons, and accordingly, it isapparent that the charged particles in the pellets are not electrons orholes but ions, more specifically, protons in consideration of theconfiguration of the fullerene derivative.

The conductivity of the above-described charged particles can becalculated on the basis of an intercept of the circular-arc on the highfrequency side with the X-axis. For the pellet of Inventive Example 1,the conductivity of the charged particles become about 5×10⁻⁶ S/cm. Thepellets of Inventive Examples 2 and 3 were subjected to the samemeasurement as described above. As a result, the whole shape of thefrequency characteristics of the impedance in each of the InventiveExamples 2 and 3 is similar to that in Inventive example 1; however, asshown in Table 1, the conductivity of charged particles in each ofInventive Examples 2 and 3, obtained on the basis of an intercept of acircular-arc portion with the X-axis, is different than in InventiveExample 1.

TABLE 1 Conductivities of Pellets of Proton Conductors in InventiveExamples 1, 2 and 3 (at 25° C.) Kind of Pellets Conductivity (S/cm)Inventive Example 1 5 × 10⁻⁶ Inventive Example 2 9 × 10⁻⁴ InventiveExample 3 2 × 10⁻⁵

As shown in Table 1, the conductivity of the pellet of the fullerenederivative containing the —OSO₃H groups cause ionization of hydrogeneasier than the hydroxyl groups. The results of Table 1 also show thatthe aggregate of the fullerene derivative containing the hydroxyl groupsand OSO₃H groups can exhibit, in a dry atmosphere, a good protonconductivity at ordinary temperature.

Next, the complex impedance of the pellet produced in Inventive Example1 was measured in a temperature range from 160° C. to −40° C., and theconductivity of the pellet was calculated on the basis of a circular-arcportion on the high frequency side of the complex impedance curve of thepellet measured at each temperature to examine the temperaturedependency on the conductivity. As the results shown in FIG. 12 (theArrhenius plot), it is apparent that the conductivity changed in astraight-line or linear fashion with respect to a change in temperaturewithin the measured temperature range of 160° C. to −40° C. In otherwords, data of FIG. 12 shows that a single ion conduction mechanism canoccur at least within the temperature range of 160° C. to −40° C. Theproton conductor mainly containing the fullerene derivative according tothe present invention, therefore, can exhibit a good proton conductivityin a wide temperature range from −40° C. to 160° C. that includesordinary temperatures.

<Forming a Film Including Polyhydroxylated Fullerene of Example 1 andGenerating Electricity Experiment Using the Film>

0.5 g of the powder of the polyhydroxylated fullerene was mixed with 1 gof tetrahydrofurane (THF), and the mixture was ultrasonic-vibrated for10 minutes, resulting in the complete dissolution of thepolyhydroxylated fullerene in THF. After fabricating a carbon electrode,a film of the polyhydroxylated fullerene was formed by the steps of:masking the surface of the electrode by a plastic mask having arectangular opening, dripping the above-described solution in theopening, spreading the solution in the opening, drying in a roomtemperature in order to vaporize THF, and removing the mask. The sameamount of electrode described above, with its downward surface having acatalyst, was laid on the film. The upper electrode was pressed by about5 tons/cm² to complete a composite. This composite was incorporated in afuel cell as shown in FIG. 9. A generating electricity experiment wasperformed by supplying hydrogen gas to one electrode and air to anotherelectrode in the fuel cell.

The experimental result is shown in FIG. 13. The open circuit voltagewas about 1.2V, and the characteristic of the closed circuit voltage wasalso excellent against the current value for the fuel cell.

II. Fullerene Derivative and Polymer Material

<Production (Part A) of Pellet of Polyhydroxylated Fullerene and PolymerMaterial>

First, 70 mg of the powder of the fullerene derivative obtained by theabove-described synthesis was mixed with 10 mg of a powder ofpolyvinylidene fluoride, followed by addition of 0.5 ml ofdimethylformamide thereto, and the powders thus mixed were stirred inthe solvent. The mixture was poured in a circular mold having a diameterof 15 mm, and the solvent was evaporated under a reduced pressure. Themixture from which the solvent was evaporated was then pressed into apellet having a diameter of 15 mm and a diameter of about 300 μm. Such apellet is taken as a pellet 1A of Inventive Example 4.

<Production (Part B) of Pellet of Polyhydroxylated Fullerene and PolymerMaterial>

Similarly, 70 mg of the powder of the fullerene derivative was mixedwith a dispersion containing 60% of a fine powder ofpolytetrafluoroethylene (PTFE) in such a manner that the content of PTFEbecame 1 wt % on the basis of the total amount, and kneaded. The mixturethus kneaded was molded into a pellet having a diameter of 15 mm and athickness of about 300 μm. Such a pellet is taken as a pellet 1B ofInventive Example 4.

<Synthesis (Part 1) of Poly-hydrogen-sulfated Fullerene>

The synthesis of a poly-hydrogen-sulfated fullerene was performed withreference to the above-described document. First, 1 g of the powder of apolyhydroxylated fullerene was put in 60 ml of fuming sulfuric acid, andwas stirred for three days while kept in a nitrogen atmosphere atordinary temperature. The reactant was put little by little in diethylether anhydride cooled in an ice bath, and the deposit was fractionatedby centrifugal separation, cleaned three times by diethyl ether andtwice by a mixture of diethyl ether and acetonitrile at a mixing ratioof 2:1, and dried under a reduced pressure at 40° C. A powder thusobtained was subjected to FT-IR measurement. As a result, the IRspectrum of the powder nearly conformed to that of a fullerenederivative in which the hydroxyl groups were all hydrogen sulfate groupsshown in the document, and therefore, it was confirmed that the powderwas the poly-hydrogen-sulfated fullerene as the target material.

<Production (Part 1A) of Pellet of Hydrogen Sulfated Fullerene andPolymer Material>

First, 70 mg of the powder of the poly-hydrogen-sulfated fullerenederivative was mixed with 10 mg of a powder of polyvinylidene fluoride,followed by addition of 0.5 ml of dimethylformamide thereto, and thepowders thus mixed were stirred in the solvent. The mixture was pouredin a circular mold having a diameter of 15 mm, and the solvent wasevaporated under a reduced pressure. The mixture from which the solventwas evaporated was then pressed into a pellet having a diameter of 15 mmand a thickness of about 300 μm. Such a pellet is taken as a pellet of2A of Inventive Example 5.

<Production (Part 1B) of Pellet of Hydrogen Sulfated Fullerene andPolymer Material>

Similarly, 70 mg of the powder of the poly-hydrogen-sulfated fullerenewas mixed with a dispersion containing 60% of a fine powder ofpolytetrafluoroethylene (PTFE) in such a manner that the content of PTFEbecame 1 wt % on the basis of the total amount, and kneaded. The mixturethus kneaded was molded into a pellet having a diameter of 15 mm and athickness of about 300 μm. Such a pellet is taken as a pellet of 2B ofInventive Example 5.

<Synthesis (Part 2) of Polyhydroxyl Hydrogen Sulfated Fullerene>

First, 2 g of a powder of a mixture of C₆₀ and C₇₀ containing about 15%of C₇₀ was put in 30 ml of fuming sulfuric acid, and was stirred forthree days while being kept in a nitrogen atmosphere at 60° C. Thereactant was put little by little in diethyl ether cooled in an icebath. It should be noted that diethyl ether not subjected to dehydrationis used. The deposit thus obtained was fractionated by centrifugalseparation, cleaned three times by diethyl ether and twice by a mixtureof diethyl ether and acetonitrile at a mixing ratio of 2:1, and driedunder a reduced pressure at 40° C. A powder thus obtained was subjectedto FT-IR measurement. As a result, the IR spectrum of the powder nearlyconformed to that of a fullerene derivative containing the hydroxylgroups and OSO₃H groups shown in the document, and therefore, it wasconfirmed that the powder was the polyhydroxyl hydrogen sulfatedfullerene as the target material.

<Production (Part 2A) of Pellet of Polyhydroxyl Hydrogen SulfatedFullerene and Polymer Material>

First, 70 mg of a powder of the polyhydroxyl hydrogen sulfated fullerenederivative was mixed with 10 mg of a powder of polyvinylidene fluoride,followed by addition of 0.5 ml of dimethylformamide thereto, and thepowders thus mixed were stirred in the solvent. The mixture was pouredin a circular mold having a diameter of 15 mm, and the solvent wasevaporated under a reduced pressure. The mixture from which the solventwas evaporated was then pressed into a pellet having a diameter of 15 mmand a thickness of about 300 μm. Such a pellet is taken as a pellet of3A of Inventive Example 6.

<Production (Part 2B) of Pellet of polyhydroxylated Hydrogen SulfatedFullerene and Polymer Material>

Similarly, 70 mg of the powder of the polyhydroxylated hydrogen sulfatedfullerene was mixed with a dispersion containing 60% of a fine powder ofpolytetrafluoroethylene (PTFE) in such a manner that the content of PTFEbecame 1 wt % on the basis of the total amount, and kneaded. The mixturethus kneaded was molded into a pellet having a diameter of 15 mm and athickness of about 300 μm. Such a pellet is taken as a pellet of 3B ofInventive Example 6.

<Production (Part A) of Pellet of Fullerene>

For comparison, 90 mg of a powder of the fullerene molecules used as theraw material for the synthesis in the above examples was mixed with 10mg of a powder of polyvinylidene fluoride, followed by addition of 0.5ml of dimethylformamide thereto, and the powders thus mixed were stirredin the solvent. The mixture was poured in a circular mold having adiameter of 15 mm, and the solvent was evaporated under a reducedpressure. The mixture from which the solvent was evaporated was thenpressed into a pellet having a diameter of 15 mm and a thickness ofabout 300 μm. Such a pellet is taken as a pellet of Comparative Example2.

<Production (Part B) of Pellet of Fullerene>

For comparison, 70 mg of the powder of the fullerene molecules used asthe raw material for synthesis in the above examples was mixed with adispersion containing 60% of a fine powder of polytetrafluoroethylene(PTFE) in such a manner that the content of PTFE became 1 wt % on thebasis of the total amount, and kneaded. The mixture thus kneaded wasmolded into a pellet having a diameter of 15 mm and a thickness of about300 μm. Such a pellet is taken as a pellet of Comparative Example 3.

<Measurement of Proton Conductivities of Pellets of Inventive Examplesand Comparative Example>

To measure a proton conductivity of each of the pellets of InventiveExample 4-6 and Comparative Example 2, both sides of the pellet wereheld between aluminum plates each having the same diameter as that ofthe pellet, that is, 15 mm, and AC voltages (amplitude: 0.1 V) atfrequencies ranging from 7 MHz to 0.01 Hz are applied to the pellet, tomeasure a complex impedance at each frequency. The measurement wasperformed under a dry atmosphere.

With respect to the above impedance measurement, a proton conductingportion 1 of a proton conductor composed of the above pelletelectrically constitutes an equivalent circuit shown in FIG. 10A, inwhich capacitances 6 and 6′ are formed between first and secondelectrodes 2 and 3 with the proton conducting portion 1 expressed by aparallel circuit of a resistance 4 and a capacitance 5 heldtherebetween. In addition, the capacitance 5 designates a delay effect(phase delay at a high frequency) upon migration of protons, and theresistance 4 designates a parameter of difficulty of migration ofprotons. The measured impedance Z is expressed by an equation ofZ=Re(Z)+i·Im(Z). The frequency dependency on the proton conductingportion expressed by the above equivalent circuit was examined. Inaddition, FIG. 10B shows an equivalent circuit of a proton conductor(Comparative Example to be described later) using the typical fullerenemolecules that contain no functional groups capable of dissociating ortransferring protons.

FIG. 14 shows results of measuring the impedances of the pellet 1A ofInventive Example 4 and the pellet of Comparative Example 2.

Referring to FIG. 14, for the pellet of Comparative Example 2, thefrequency characteristics of the complex impedance is nearly the same asthe behavior of a single capacitor, and the conductance of chargedparticles (electrons, ions and the like) of the aggregate of thefullerene molecules is not observed at all; while, for the pellet 1A ofInventive Example 4, the impedance in a high frequency region depicts aflattened but very smooth single semi-circular arc, which shows theconductance of some charged particles in the pellet, and the imaginarynumber portion of the impedance is rapidly raised in a low frequencyregion, which shows the occurrence of blocking of charged particlesbetween the aluminum electrode and the pellet as gradually nearing theDC voltage. With respect to the blocking of the charged particlesbetween the aluminum electrode and the pellet 1A of Inventive Example 4,the charged particles on the aluminum electrode side are electrons, andaccordingly, it is apparent that the charged particles in the pelletsare not electrons or holes but ions, more specifically, protons inconsideration of the configuration of the fullerene derivative.

The conductivity of the above-described charged particles can becalculated on the basis of an intercept of the circular-arc on the highfrequency side with the X-axis. For the pellet 1A of Inventive Example4, the conductivity of the charged particles become about 1×10⁻⁶ S/cm.The pellets of 1B of Inventive Example 4, the pellets 2A and 2B ofInventive Example 5, and the pellets of 3A and 3B of Inventive Example 6were subjected to the same measurement as described above. As a result,the whole shape of the frequency characteristics of the impedance ineach of the pellets 1B, 2A and 2B, and 3A and 3B is similar to that of1A of Inventive Example 4; however, as shown in Table 2, theconductivity of charged particles in each of the pellets of 1B, 2A and2B, and 3A and 3B, obtained on the basis of an intercept of acircular-arc portion with the X-axis, is different from that in thepellet 1A.

TABLE 2 Conductivities of Pellets of Proton Conductors in InventiveExamples 4, 5 and 6 (at 25° C.) Kind of Pellets Conductivity (S/cm)Pellet 1A of Inventive Example 4 1 × 10⁻⁶ Pellet 2A of Inventive Example5 2 × 10⁻⁴ Pellet 3A of Inventive Example 6 6 × 10⁻⁵ Pellet 1B ofInventive Example 4 3 × 10⁻⁶ Pellet 2B of Inventive Example 5 7 × 10⁻⁴Pellet 3B of Inventive Example 6 3 × 10⁻⁶

As shown in Table 2, in both of the pellet types A and B of theInventive Examples 4, 5, and 6, the conductivity of the pellet of thefullerene derivative containing the OSO₃H groups is larger than that ofthe pellet of the fullerene derivative containing the hydroxyl groups.The reason for this is that the OSO₃H groups cause ionization ofhydrogen more easily than the hydroxyl groups. The results of Table 2also show that the aggregate of the fullerene derivative containing thehydroxyl groups and OSO₃H groups can exhibit, in a dry atmosphere, agood proton conductivity at ordinary temperature.

Next, the complex impedance of the pellet 1A of Inventive Example 4 wasmeasured in a temperature range from 160° C. to −40° C., and theconductivity of the pellet was calculated on the basis of a circular-arcportion on the high frequency side of the complex impedance curve of thepellet measured at each temperature to examine the temperaturedependency on the conductivity. The results are shown in FIG. 15 as theArrhenius plot. From the data shown in FIG. 15, it is apparent that theconductivity and temperature exist in a linear relationship at leastwithin the temperature range of 160° C. to −40° C. In other words, dataof FIG. 15 shows that a single ion conduction mechanism can proceed inthe temperature range of 160° C. to −40° C. The proton conductor mainlycontaining the fullerene derivative and a polymer material according tothe present invention, therefore, can exhibit a good proton conductivityin a wide temperature range including ordinary temperature,particularly, ranging from a high temperature of 160° C. to a lowtemperature of −40° C.

III. Carbon Cluster Derivative

<Production (Part 1) of Carbon Cluster Derivative>

Arc discharge was performed by applying a current of 200 A between bothelectrodes composed of carbon bars in 0.05 MPa of an argon, to thusobtain 1 g of a carbon powder. The carbon powder was mixed with 100 mlof 60% fuming sulfuric acid, and kept for three days in a nitrogen flowat 60° C. The heating was performed by using a water bath. The reactionsolution was dropped little by little in 500 ml of pure water, and asolid matter was separated from the water solution by centrifugalseparation method. The solid matter was cleaned several times by diethylether anhydride, and dried for five hours under a reduced pressure at40° C. The resultant powder was dissolved in 10 ml of tetrahydrofurane(THP), an insoluble component removed by filtering, and the solvent wasevaporated under a reduced pressure to obtain a solid matter wherein thesolid matter of 50 mg was pressed at a force of 7 tons/cm² into acircular pellet having a diameter of 15 mm. Such a pellet is taken as apellet of Inventive Example 7.

<Measurement of Proton Conductivity of Pellet of Carbon ClusterDerivative>

The AC impedance of the pellet of Inventive Example 7 was measured in adry air in accordance with the same manner as described above. As aresult, it was confirmed that an impedance behavior resulting from ionconductance appeared in a frequency region of 10 MHz or less. Theconductivity of the pellet of Inventive Example 7 was calculated, on thebasis of the diameter of a circular-arc curve of the impedance behavior,at 3.0×10⁻⁴(S/cm).

<Production (Part 2) of Carbon Cluster Derivative>

Arc discharge was performed by applying a current of 200 A between bothelectrodes composed of carbon bars in 0.05 MPa of an argon gas, to thusobtain 1 g of a carbon powder. The carbon powder was dissolved intoluene, an insoluble component was removed by filtering, and thesolvent was evaporated under a reduced pressure to obtain a powderagain. The resultant powder was mixed with 100 ml of 60% fuming sulfuricacid, and kept for three days under a nitrogen flow at 60° C. Theheating was performed by using a water bath. The reaction solution wasdropped little by little in 500 ml of pure water, and a solid matter wasseparated from the water solution by centrifugal separation method. Thesolid matter was cleaned several times by diethyl ether anhydride, anddried for five hours under a reduced pressure at 40° C. The solid matterof 50 mg was under a force of 7 tons/cm² into a circular pellet ofInventive Example 8.

<Measurement of Proton Conductivity of Pellet of Carbon ClusterDerivative>

The AC impedance of the pellet of Inventive Example 8 was measured in adry air in accordance with the same manner as described above. As aresult, it was confirmed that an impedance behavior resulting from ionconductance appeared in a frequency region of 10 MHz or less. Theconductivity of the pellet of Inventive Example 8 was calculated, on thebasis of the diameter of a circular-arc curve of the impedance behavior,at 3.4×10⁻⁴(S/cm).

The main component of the carbon powder obtained by arc discharge wascarbon clusters or molecules of carbon clusters not having a closedstructure, such as, a cage structure, but having a structure at leastpart of which has open ends. In addition, molecules having a structurewith good electronic conductivity, similar to the graphite structure,which are slightly contained in the carbon cluster molecules, oftenobstruct the function of the ionic conductor and thereby they areremoved after acid treatment in Inventive Example 7 and directly afterarc discharge in Inventive Example 8. As a result, it was confirmed bythe AC impedance method that the pellet has no electronic conductivity.FIG. 16 shows the TOF-MS spectrum of carbon powder obtained by arcdischarge. As shown in FIG. 16, most of the carbon powder has a massnumber of 5500 or less, that is, the carbon number of 500 or less. Sincethe carbon-carbon bonding distance of the carbon powder is less than 2Å, the diameter of each of the carbon clusters of the powder is lessthan 100 nm.

IV. Tubular Carbonaceous Material Derivative

<Synthesis (Part 1) of a Polyhydroxylated SWCNT Material>

A refined SWCNT material was prepared and then burned for ten hours at250° C. under a fluorine gas in order to obtain polyfluorinated SWCNT.The polyfluorinated SWCNT was placed in pure water and refluxed forthree days at 100° C. while being strongly stirred in order tosubstitute the fluorine atoms for hydroxyl groups thereby resulting inthe polyhydroxylated SWCNT material which is identified as a material inInventive Example 9.

<Synthesis of Hydrogen Sulfated SWCNT>

Polyhydroxylated SWCNT produced in the same manner as that in InventiveExample 9 was placed in fuming sulfuric acid and stirred for three daysat 60° C. in order to replace the hydroxyl groups with the OSO₃H groupsthereby resulting in the hydrogen sulfated SWCNT material as identifiedin Inventive Example 10.

<Synthesis (Part 2) of Polyhydroxylated SWCNT>

A refined SWCNT material was prepared and then subjected to oxygenplasma treatment. Then, the atmosphere in the chamber was replaced withhydrogen and the material was subsequently subjected to hydrogen plasmatreatment in order to obtain the polyhydroxylated SWCNT material asidentified as Inventive Example 11.

<Production of Sample Films>

Each of the above three materials was dispersed in water and thedispersion was filtered on a filter paper having pores of 0.2 μm bysuction in order to deposit the film on the filter paper. The amount ofthe dispersion to be filtered was adjusted to form the film having athickness of 100 μm. The film deposited on the filter paper could beeasily peeled therefrom. These films thus obtained are taken as films inInventive Examples 9, 10 and 11. A material obtained by mixing thematerial in Inventive Example 10 with a poly-hydrogen-sulfated fullerenederivative at a weight ratio of 1:1 was filtered in the same manner asdescribed above to form a film as identified in Inventive Example 12.Further, an SWCNT material that contains no functional groups wasfiltered in the same manner as described above to form the film which isidentified as Comparative Example 4.

<Measurement of Proton Conductivities of the Film>

To measure a proton conductivity of each of the films in InventiveExamples 9 to 12 and Comparative Example 4 both sides of the film wereheld between aluminum foil which were cut into a disc shape having adiameter 15 mm. The disc was held between electrodes, and AC voltages(amplitude: 0.1 V) at frequencies ranging from 7 MHz to 0.01 Hz wereapplied to the film to measure a complex impedance at each frequency.The measurement was performed under a dry atmosphere.

The measurement result of the film in Comparative Example 4 will bedescribed below. The complex impedance of the film was fixed at a lowresistance, that is, was not changed over the above frequency range dueto the fact that the electronic conductivity of the SWCNT material ofComparative Example 4 is high.

As a result, it was revealed that the film in Comparative Example 4cannot be used as an ionic conductor.

The measurement results of the films in Inventive Examples 9-12 will bedescribed below. A complex impedance of the film of Inventive Example 10is representatively shown in FIG. 26. Referring to FIG. 26, theimpedance in a high frequency region depicts a flattened but very smoothsemi-circular curve, which shows the conductance of some chargedparticles in the film and the imaginary number portion of the impedanceis rapidly raised in a low frequency region, which shows the occurrenceof the blocking of charged particles between the aluminum electrodes andthe film as gradually nearing to a DC voltage.

With respect to the blocking of the charged particles between thealuminum electrode and the film in Inventive Example 10, the chargedparticles on the aluminum electrode side are electrons, and accordingly,it is apparent that the charged particles in the film are not electronsor holes but ions, more specifically, protons in considering of thestructure of the tubular carbonaceous derivative that forms the film.

With respect to the films in Inventive Examples 9, 11 and 12, thebehavior of these films are similar to that of the film in InventiveExample 10 as observed although there was a difference in the size ofthe circular arc therebetween. Accordingly, it was revealed that thefilms in Inventive Examples 9-12 desirably function as a tubularcarbonaceous material derivative of a proton conductor.

With respect to the above impedance measurements, the proton conductingportion 1 of the film-like proton conductor constitutes an electricallyequivalent circuit in which a capacitance is formed between first andsecond electrodes with a resistance in the proton conducting portionheld therebetween as similarly identified in the previously discussedembodiments and as further illustrated in FIG. 10A. In addition, thecapacitance designates a delay effect (phase delay at a high frequency)upon migration of protons, and the resistance designates a parameter ofdifficulty of migration of protons. The measured impedance Z isexpressed by the equation as previously discussed in other embodiments.The frequency dependency on the proton conductivity portion wasexamined.

The conductivity of the above described charged particles can becalculated on the basis of an intercept of the circular-arc on the highfrequency side of with the X-axis. The conductivity of the film inInventive Example 10 is about 2×10⁻⁵ S/cm. The conductivities of thefilm in Inventive Examples 9, 11, and 12 are 2×10⁻⁷ S/cm, 7×10⁻⁸ (S/cm)and 8×10³¹ ⁴ (S/cm), respectively. The conductivity for each ofInventive Examples 9-12 were measure at 25° C.

In comparing the conductivity of Inventive Examples 9-12, it is apparentthat the tubular carbonaceous material derivative that contain thehydrogen sulfated functional groups, i.e. the —OSO₃H groups, are largerthan the conductivity of the tubular carbonaceous material derivativethat contain the hydroxyl groups. The reason for this difference wasdiscussed in relation to previous embodiment of the present invention.The comparison of Inventive Examples 9-12 also demonstrates that theaggregate of the tubular carbonaceous material derivative that containseither or both of the hydroxyl and hydrogen sulfated groups, even in adry atmosphere, desirably displays a proton conductivity at ordinarytemperatures.

As is apparent from the above description, since the first protonconductor according to the first embodiment mainly contains a fullerenederivative that includes functional groups, it can exhibit a high protonconductivity, even in a dry state, in a wide temperature range includingordinary temperature. Since the electrochemical device using the firstproton conductor is not limited by an atmosphere, its construction canbe simplified and minimized in size.

Since the first proton conductor can be produced of a fullerenederivative, it is possible to efficiently produce the first protonconductor without use of any binder resin, and hence to enhance theproton conductivity of the first proton conductor and reduce the weightthereof.

Since the second proton conductor according to the second embodiment canbe obtained by mixing the fullerene derivative with a polymer material,a high film formation ability can be given, together with the aboveperformance of the first proton conductor, to the second protonconductor, so that the second proton conductor can be used as a thinfilm having a high strength, a good gas permeation preventative abilityand a high proton conductivity. The electrochemical device, such as, afuel cell using the second proton conductor has a performance comparableto that of the electrochemical device using the first proton conductor,and also exhibits the effect of the second proton conductor in the formof a thin film.

Since the third proton conductor according to the third embodimentmainly contains a carbon cluster derivative in which functional groupsare introduced to each of the carbon clusters which are the basematerial of the carbon cluster derivative, it can exhibit effectssimilar to those obtained by each of the first and second embodiments interms of proton conductivity, operation temperature, simplification ofthe system, miniaturization and economy. Further, since each carboncluster contains a large number of carbon atoms closely bonded to eachother, it is less susceptible to deterioration by oxidation, and isadvantageous in that the selection range of the raw material can beextended.

Since the fourth proton conductor according to the fourth embodimentmainly contains a tubular carbonaceous material derivative that includesa number of functional groups, this type of proton conductor can exhibitdesirable effects that are similar to those which were demonstrated andobtained by each of the first, second and third embodiments with regardsto proton conductivity, operation temperature, simplification ofconstruction, miniaturization, and economy for a fuel cell using theproton conductor. Further, according to the present invention asdetailed in the fourth embodiment, a tubular carbonaceous materialderivative film that has high strength and good proton conductivity isdesirably suitable for an electrochemical device, in particular, a fuelcell. This film can be obtained by dispersing the tubular carbonaceousmaterial derivative in a liquid and filtering the dispersion.

Although modifications and changes may be suggested by those skilled inthe art, it is the intention of the inventors to embody within thepatent warranted hereon all changes and modifications as reasonably andproperly come within their contribution to the art.

We claim as our invention:
 1. A method of producing a proton conductor,comprising the steps of: forming a carbon powder by producing aplurality of carbon clusters that each include a plurality of carbonatoms by an arc discharge technique that utilizes a carbon-basedelectrode; subjecting the carbon powder to an acid treatment; andintroducing a plurality of functional groups to the carbon powder so asthe carbon powder is capable of transferring protons between each of thefunctional groups of the carbon powder.
 2. A method of producing aproton conductor according to claim 1, further comprising the steps offorming a carbon cluster derivative by introducing the functional groupsto the carbon powder, and compacting the carbon cluster derivative intoa desired shape.
 3. A method of producing a proton conductor accordingto claim 1, wherein the compacting step comprises the step of formingthe carbon cluster derivative into a pellet shape without the use of anybinder.
 4. A method of producing a proton conductor according to claim1, wherein the functional groups are represented by —XH where X is anarbitrary atom or an atomic group that has a bivalent bond and where His a hydrogen atom.
 5. A method of producing a proton conductoraccording to claim 1, wherein the functional groups are expressed by —OHor —YOH where Y is an arbitrary atom or an atomic group that has abivalent bond, where O is an oxygen atom and where H is a hydrogen atom.6. A method of producing a proton conductor according to claim 5,wherein the functional groups are selected from the group consisting of—OH, —OSO₃H, —COOH, —SO₃H, and —OPO(OH)₃.
 7. A method of producing aproton conductor according to claim 1, further comprising the step ofintroducing a plurality of electron attractive groups to the carbonpowder in addition to the functional groups.
 8. A method of producing aproton conductor according to claim 7, wherein the electron attractivegroups are selected from the group consisting of nitro groups, carbonylgroups, carboxyl groups, nitrile groups, alkyl halide groups and halogenatoms.
 9. A method of producing a proton conductor according to claim 1,wherein the carbon powder comprises a cluster that substantiallyincludes a plurality of carbon atoms, the cluster comprises a lengthalong a major axis of 100 nm or less, and wherein two or more functionalgroups are introduced to the cluster.
 10. A method of producing a protonconductor according to claim 1, wherein the carbon powder comprises aspherical carbon cluster that is expressed by C_(m) wherein m represents36, 60, 70, 78 or
 82. 11. A method of producing a proton conductoraccording to claim 1, wherein the carbon powder comprises a cluster thathas a cage structure or a structure at least part of which has openends.
 12. A method of producing a proton conductor according to claim 1,further comprising the step of mixing the carbon powder with a polymermaterial so as to form a thin film or a pellet construction.
 13. Amethod of producing a proton conductor according to claim 12, whereinthe polymer material comprises no electronic conductivity.
 14. A methodof producing a proton conductor according to claim 12, wherein thepolymer material comprises a polymer material compound that is selectedfrom the group consisting of at least one of polyfluoroethylene,polyvinylidene fluoride, and polyvinylalcohol.
 15. A method of producinga proton conductor according to claim 12, wherein the polymer materialcomprises 20 wt % or less.
 16. A method of producing a proton conductoraccording to claim 12, wherein the polymer material comprisespolyfluoroethylene of 3 wt % or less.
 17. A method of producing a protonconductor according to claim 12, wherein the proton conductor comprisesa thin film that has a thickness of 300 μm or less.
 18. A method ofproducing a proton conductor, comprising the steps of: producing afullerene derivative by introducing a plurality of functional groups toa plurality of fullerene molecules of the fullerene derivative; forminga powder of the fullerene derivative; and compacting the powder into adesired shape.
 19. A method or producing a proton conductor according toclaim 18, wherein the compacting step comprises the step of forming apowder of the fullerene derivative into a pellet without the use of anybinder.
 20. A method or producing a proton conductor according to claim18, wherein the functional groups are expressed by —XH where X is anarbitrary atom or an atomic group that has a bivalent bond and where His a hydrogen atom.
 21. A method or producing a proton conductoraccording to claim 18, wherein the functional groups are expressed by—OH or —YOH where Y is an arbitrary atom or an atomic group that hasbivalent bond, where O is an oxygen atom and where H is a hydrogen atom.22. A method or producing a proton conductor according to claim 22,wherein the functional groups are selected from the group consisting of—OH, —OSO₃H, —COOH, —SO₃H, and —OPO(OH)₃.
 23. A method or producing aproton conductor according to claim 22, wherein the step of producingthe fullerene derivative further comprises the step of introducing aplurality of electron attractive groups to the fullerene molecules ofthe fullerene derivative in addition to the functional groups.
 24. Amethod or producing a proton conductor according to claim 23, whereinthe electron attractive groups are selected from the group consisting ofnitro groups, carbonyl groups, carboxyl groups, nitrile groups, alkylhalide groups and halogen atoms.
 25. A method or producing a protonconductor according to claim 18, wherein the fullerene derivativecomprises a spherical carbon cluster expressed by C_(m) where mrepresents 36, 60, 70, 78, 82 or
 84. 26. A method of producing a protonconductor comprising the steps of: producing a fullerene derivative byintroducing a plurality of functional groups to a plurality of fullerenemolecules of the fullerene derivative; mixing the fullerene derivativewith a polymer material; and forming the fullerene derivative andpolymer material mixture into a thin film.
 27. A method of producing aproton conductor according to claim 26, wherein the polymer material hasno electronic conductivity.
 28. A method of producing a proton conductoraccording to claim 26, wherein the functional groups are expressed by—XH where X is an arbitrary atom or an atomic group that has a bivalentbond and where H is a hydrogen atom.
 29. A method of producing a protonconductor according to claim 26, wherein the functional groups areexpressed by —OH or —YOH where Y is an arbitrary atom or an atomic groupthat has bivalent bond, where O is an oxygen atom and where H is ahydrogen atom.
 30. A method of producing a proton conductor according toclaim 29, wherein the functional groups are selected from the groupconsisting of —OH, —OSO₃H, —COOH, —SO₃H, and —OPO(OH)₃.
 31. A method ofproducing a proton conductor according to claim 26, wherein a pluralityof electron attractive groups are further introduced to the fullerenederivative in addition to the functional groups.
 32. A method ofproducing a proton conductor according to claim 31, wherein the electronattractive groups are selected from the group consisting of at least oneof nitro groups, carbonyl groups, carboxyl groups, nitrile groups, alkylhalide groups and halogen atoms.
 33. A method of producing a protonconductor according to claim 26, wherein the fullerene derivativecomprises a spherical carbon cluster material expressed by C_(m) where mrepresents 36, 60, 70, 78, 82 or
 84. 34. A method of producing a protonconductor according to claim 26, wherein the polymer material comprisesa polymer material compound that is selected from the group consistingof polyfluoroethylene, polyvinylidene fluoride, and polyvinylalcohol.35. A method of producing a proton conductor according to claim 26,wherein the polymer material comprises 20 wt % or less.
 36. A method ofproducing a proton conductor according to claim 26, wherein the polymermaterial comprises polyfluoroethylene of 3 wt % or less.
 37. A method ofproducing a proton conductor according to claim 26, wherein the protonconductor comprises a thin film that has a thickness of 300 μm or less.38. A method of producing a proton conductor, comprising the steps of:preparing one of a halogenated or non-halogenated tubular carbonaceousmaterial as a raw material; and forming a tubular carbonaceous materialderivative by introducing a plurality of functional groups onto the rawmaterial by subjecting the raw material to hydrolysis or an acidtreatment or hydrolysis and an acid treatment or a plasma treatment. 39.A method of producing a proton conductor according to claim 38, furthercomprising subjecting the halogenated tubular carbonaceous material tohydrolysis or an acid treatment or hydrolysis and an acid treatment soas to form the tubular carbonaceous material derivative or subjectingthe non-halogenated tubular carbonaceous material to the plasmatreatment so as to form the tubular carbonaceous material derivative.40. A method of producing a proton conductor according to claim 38,wherein the functional groups are expressed by —XH where X is anarbitrary atom or an atomic group that has a bivalent bond and where His a hydrogen atom.
 41. A method of producing a proton conductoraccording to claim 38, wherein the functional groups comprise —OH or—YOH where Y is an arbitrary atom or an atomic group that has bivalentbond, where O is an oxygen atom and where H is a hydrogen atom.
 42. Amethod of producing a proton conductor according to claim 41, whereinthe functional groups are selected from the group consisting of —OH,—OSO₃H, —COOH, —SO₃H, and —OPO(OH)₃.
 43. A method of producing a protonconductor according to claim 38, further comprising introducing aplurality of electron attractive groups in addition to the functionalgroups to the tubular carbonaceous material of the tubular carbonaceousmaterial derivative.
 44. A method of producing a proton conductoraccording to claim 43, wherein the electron attractive groups areselected from the group consisting of nitro groups, carbonyl groups,carboxyl groups, nitrile groups, alkyl halide groups and halogen atoms.45. A method of producing a proton conductor according to claim 38,wherein the tubular carbonaceous material derivative comprises a tubularcarbonaceous material that includes a single-wall carbon nano-tubematerial.
 46. A method of producing a proton conductor according toclaim 38, wherein the tubular carbonaceous material derivative comprisesa tubular carbonaceous material that includes a multi-wall carbonnano-tube material.
 47. A method of producing a proton conductoraccording to claim 38, wherein the tubular carbonaceous materialderivative comprises a tubular carbonaceous material that includes acarbon nano-fiber material.
 48. A method of producing a proton conductoraccording to claim 38, wherein the halogenated tubular carbonaceousmaterial derivative comprises a fluoride.
 49. A method of producing aproton conductor according to claim 38, further comprising the step ofdispersing the tubular carbonaceous material derivative within a liquid,and filtering the dispersion of the tubular carbonaceous materialderivative so as to form a film.